1. Field of the Invention
The present invention generally relates to copy-protected optical information recording media and methods for manufacturing the same. More specifically, the present invention relates to the manufacture of an optically readable digital storage medium that protects the information stored thereon from being copied using conventional optical medium readers, such as CD and DVD laser readers, but permits reading of the information from the digital storage media by the same readers.
2. Background of the Invention
Data is stored on optical media by forming optical deformations or marks at discrete locations in one or more layers of the medium. Such deformations or marks effectuate changes in light reflectivity. To read the data on an optical medium, an optical medium player or reader is used. An optical medium player or reader conventionally shines a small spot of laser light, the “readout” spot, through the disc substrate onto the data layer containing such optical deformations or marks as the medium or laser head rotates.
In conventional “read-only” type optical media (e.g., “CD-ROM”), data is generally stored as a series of “pits” embossed in a plane of “lands”. Microscopic pits formed in the surface of the plastic medium are arranged in tracks, conventionally spaced radially from the center hub in a spiral track originating at the medium center hub and ending toward the medium's outer rim. The pitted side of the medium is coated with a reflectance layer such as a thin layer of aluminum or gold. A lacquer layer is typically coated thereon as a protective layer.
It is important to note that various nomenclature are used in the art to describe the information-bearing structure formed in read-only type optical media. Often when referenced from the laser-read side, the pits are referred to as “bumps”. However, sometimes “lands” from the non-read side are referred to as “pits” from the read-side and “pits” from the non-read side are referred to as “lands” from the read-side. Those skilled in the art would understand from context which structures are being referenced when viewing is described from the read or non-read sides. However, to provide consistency in use, the terms “pits” and “lands” are used throughout this disclosure in conformity with their definitions set forth below.
A readout spot directed from the non-metalized side is reflected in a manner that the light of the readout spot is reflected back into a photo-sensor in the reader. The transitions between pits and lands, and the timing in between such transitions, represent channel bits. Thus, the pits and lands in themselves are not representations of a sequence of zeros or ones.
The intensity of the light reflected from a read-only medium's surface measured by an optical medium player or reader varies according to the presence or absence of pits and lands along the information track. When the readout spot is over a land, more light is reflected directly from the disc than when the readout spot is over a pit. A photo-detector and other electronics inside the optical medium player translate the signal from the transition points between these pits and lands caused by this variation into the 0s and 1s of the digital code representing the stored information.
The vast majority of commercially-available software, video, audio, and entertainment pieces available today are recorded in read-only optical format. One reason for this is that data replication onto read-only optical formats is significantly cheaper than data replication onto writable and rewritable optical formats. Another reason is that read-only formats are less problematical from a reading reliability standpoint. For example, some CD readers/players have trouble reading CD-R media, which has a lower reflectivity and thus requires a higher-powered reading laser or one that is better “tuned” to a specific wavelength.
Interference/reflectivity type optical media comprising a read-only format are typically manufactured following a number of defined steps:
Data to be encoded on the read-only optical medium is first pre-mastered (formatted) such that data can be converted into a series of laser bursts by a laser, which will be directed onto a glass master platter. The glass master platter is conventionally coated with a photoresist such that when the laser beam from the LBR (laser beam recorder) hits the glass master a portion of the photoresist coat is “burnt” or exposed. After being exposed to the laser beam, it is cured and the photoresist in the unexposed area rinsed off. The resulting glass master is electroplated with a metal, typically Ag or Ni. The electroformed stamper medium thus formed has physical features representing the data. When large numbers of optical media of the disc-type are to be manufactured, the electroformed stamper medium is conventionally called a “father disc”. The father disc is typically used to make a mirror image “mother disc,” which is used to make a plurality of “children discs,” which are often referred to as “stampers” in the art. Stampers are used to make production quantities of replica discs, each containing the data and tracking information that was recorded on the glass master. If only a few discs are to be replicated (fewer than 10,000) and time or costs are to be conserved, the original “father” disc might be used as the stamper in the mold rather than creating an entire “stamper family” consisting of a “father”, “mother” and “children” stampers.
The stamper is typically used in a mold in conjunction with an injection molding machine to produce replica media. Commercially-available injection molding machines subject the mold to a large amount of pressure by piston-driven presses, in excess of 20,000 pounds.
In the read-only optical medium molding process, a resin is forced in through a sprue channel into a cavity within the optical tooling (mold) to form the optical medium substrate. Today most optical discs are made of optical-grade polycarbonate which is kept dry and clean to protect against reaction with moisture or other contaminants which may introduce birefringence and other problems into the disc, and which is injected into the mold in a molten state at a controlled temperature. The format of the pits and lands is replicated in the substrate by the stamper as the cavity is filled and compressed against the stamper. After the part has sufficiently cooled, the optical tooling mold is opened and the sprue and product eject are brought forward for ejecting the formed optical medium off of the stamper. The ejected substrate is handed out by a robot arm or gravity feed to the next station in the replication line, with transport time and distance between stations giving the substrate a chance to cool and harden.
The next step after molding in the manufacture of a read-only optical medium is to apply a layer of reflective metal to the data-bearing side of the substrate (the side with the pits and lands). This is generally accomplished by a sputtering process, where the plastic medium is placed in a vacuum chamber with a metal target, and electrons are shot at the target, bouncing individual molecules of the metal onto the medium, which attracts and holds them by static electricity. The sputtered medium is then removed from the sputtering chamber and spin-coated with a polymer, typically a UV-curable lacquer, over the metal to protect the metal layer from wear and corrosion. Spin-coating occurs when the dispenser measures out a quantity of the polymer onto the medium in the spin-coating chamber and the medium is spun rapidly to disperse the polymer evenly over its entire surface.
After spin-coating, the lacquer (when lacquer is used as the coat) is cured by exposing it to UV radiation from a lamp, and the media are visually inspected for reflectivity using a photodiode to ensure sufficient metal was deposited on the substrate in a sufficiently thick layer so as to permit every bit of data to be read accurately. Read-only optical media that fail the visual inspection are loaded onto a reject spindle and later discarded. Those that pass are generally taken to another station for labeling or packaging. Some of the “passed” media may be spot-checked with other testing equipment for quality assurance purposes.
Optical media of all types have greatly reduced the costs involved in selling content such as software, video and audio works, and games, due to their small size and the relatively inexpensive amount of resources involved in their production. They have also unfortunately improved the economics of the pirate, and in some media, such as video and audio, have permitted significantly better pirated-copies to be sold to the general public than permitted with other data storage media. Media distributors report the loss of billions of dollars of potential sales due to high quality copies.
Typically, a pirate makes an optical master by extracting logic data from the optical medium, copying it onto a magnetic tape, and setting the tape on a mastering apparatus. Pirates also sometimes use CD or DVD recordable medium duplicator equipment to make copies of a distributed medium, which duplicated copies can be sold directly or used as pre-masters for creating a new glass master for replication. Hundreds of thousands of pirated optical media can be pressed from a single master with no degradation in the quality of the information stored on the optical media. As consumer demand for optical media remains high, and because such medium is easily reproduced at a low cost, counterfeiting has become prevalent.
A variety of copy protection techniques and devices have been proposed in the art to limit the unauthorized copying of optical media. Among these techniques are analog Colorstripe Protection System (CPS), CGMS, Content Scrambling System (CSS) and Digital Copy Protection System (DCPS). Analog CPS (also known as Macrovision) provides a method for protecting videotapes as well as DVDs. The implementation of Analog CPS, however, may require the installation of circuitry in every player used to read the media. Typically, when an optical medium or tape is “Macrovision Protected,” the electronic circuit sends a colorburst signal to the composite video and s-video outputs of the player resulting in imperfect copies. Unfortunately, the use of Macrovision may also adversely affect normal playback quality.
There is a need therefore for a copy-protected optical medium, which does not depend entirely on encryption codes or special hardware to prevent the copying of the optical medium. Such optical media should also be easily and economically manufactured given the current strictures of optical medium manufacture. The copy-protected media should also be readable by the large number of existing optical medium readers or players without requiring modifications to those devices.